For many years industry has been interested on the one hand in alternative energy sources, which are not based on fossil deposits, and on the other hand in so-called xe2x80x9crenewable raw materialsxe2x80x9d. The latter include in particular plant oils, or in other words fatty acid esters, usually triglycerides, which in general can be classified as biodegradable and environmentally harmless. Rapeseed oil (colza oil) can be regarded as the prototype for such oils. Recommendations on application of rapeseed oil as a lubricant can be traced back to the twenties (see D. Holde, Chemiker-Zeitung 1922 (1), p. 4).
Under the impetus of environmental legislation, structural changes in agriculture and the general ecological trend, plant oils and modified plant oils such as rapeseed oil methyl ester (RME) as renewable raw materials are becoming increasingly important as fuels and heating oils. An important consideration for practical use of plant oil methyl esters (PME) is their flowability even at relatively low temperatures. Similarly to conventional diesel fuel, components of the fuel crystallize out from biodiesel at low temperatures, thus impairing filterability and flowability. The term biodiesel and biofuel oils encompasses mixtures of petrochemical base diesel oils and renewable raw materials, although the ratio of petrochemical motor fuel to renewable raw materials in the mixture can vary and is not defined. The filterability of diesel fuels is usually characterized by the CFPP value (cold filter plugging point, determined in accordance with DIN EN 116).
Depending on the type of plant oil used as basis and on the quality of modification or treatment, PMEs without additives typically have CFPP values between 0xc2x0 C. and xe2x88x9215xc2x0 C. If these were to be used as biodiesel, therefore, fouling of the fuel filter would be expected at relatively low temperatures. For example, CFPP values below xe2x88x9220xc2x0 C. are stipulated for winter diesel (DIN EN 590). Conventional fluidizing additives for diesel fuels have been found to have only limited effect in PME, and in many cases lower the CFPP temperature only slightly if at all.
German Patent DE 19603696 (Rxc3x6hm GmbH, Aug. 7, 1977) relates to demulsifiers based on polyalkyl (meth)acrylate cooligomers. The function of the demulsifiers is to destroy emulsions. They are used, for example, to separate oil from water in hydraulic oils.
French Patent FR 2589866 (French Petroleum Institute, May 15, 1987) describes copolymers of short-chain (C1-Cu), medium-chain (C8-C14) and long-chain (C16-C22) esters of methacrylic acid and a vinylaromatic component.
European Patent EP 418610 (Rxc3x6hm GmbH) describes copolymers suitable for improvement of the viscosity index of lubricating oils, which copolymers comprise 80 to 99.5 parts by weight of alkyl (meth)acrylate esterified with a long-chain alcohol and 0.5 to 20 parts by weight of a functionalized alkyl (meth)acrylate, the methacrylic acid being esterified by a C2-C6 alcohol or by a group containing multiple alkoxy units. The copolymers have good shear stability and good dispersant and detergent effect in lubricating oils.
European Patent EP 543356 (Rxc3x6hm GmbH) describes a process for synthesis of compositions with improved low-temperature behavior for use as fuels or for use as lubricants on the basis of rapeseed oil methyl ester. A mixture capable of lowering the cold filter plugging point to xe2x88x9215xc2x0 C. to xe2x88x9220xc2x0 C. is synthesized by the process according to the invention. The resulting precipitates of long-chain fatty acid esters not containing additives are filtered off.
U.S. Pat. No. 5,578,090 (BRI) describes a biodiesel additive comprising fatty acid alkyl esters, glycerol esters and triglycerides. The additive is biodegradable.
European Patent 691355 (Rxc3x6hm GmbH) describes cooligomers and copolymers with dispersant action on the basis of esters of methacrylic acid with alkoxylated alcohols having a specified content of ethylene oxide or propylene oxide units, which cooligomers and copolymers can be used as ashless dispersants in lubricating oils. The molecular weights of the cooligomers and copolymers with dispersant action range between 1000 and 300,000 daltons.
In addition to the good low-temperature characteristics, good dispersant characteristics can also be expected from these PAMAs modified with polar oxygen-containing comonomers. In other words, there can be expected an active cleaning effect, which contributes to preventing deposits in the fuel-supply system (for example, at injection nozzles).
German Patents DE 3930142 and DE 4423358 describe comparable oxygen-containing dispersant PAMAs and their good dispersant action as lubricating oil additives which simultaneously have excellent compatibility with gasket materials. These applications do not consider the unexpectedly good efficacy for use as additives for biodiesel and biofuel oils.
The object was therefore to provide additives for improvement of the low-temperature behavior, especially of the cold filter plugging point, of fatty acid esters of monohydric alcohols, especially of rapeseed oil methyl ester. As an example, the target was to lower the CFPP from xe2x88x9215xc2x0 C. to xe2x88x9222xc2x0 C. in the case of rapeseed oil methyl ester.
Another object was to develop an effective additive for control of the CFPP of RME. More particularly, the object was to achieve reliable adjustment of CFPP values of xe2x89xa620xc2x0 C. with economic additive proportions of typically xe2x89xa61 wt %. It was also anticipated that further characteristics important for the low-temperature flow behavior, such as pour point (ASTM D 92) and softening point (measured per Herzog MC 852), would be influenced favorably by the additive.
A further object in the scope of the invention was to provide mixtures of the inventive polymers and copolymers with biodiesels, which mixtures are suitable for use at low temperatures.
Industry has long used polymeric compounds, otherwise known as xe2x80x9cpour point depressantsxe2x80x9d, to lower the pour point of lubricating oils and other mineral oil products. The common structural feature of such polymers is a plurality of alkyl side chains, usually containing 8 to 40, especially 10 to 28 carbon atoms. Poly(meth)acrylic acid esters of long-chain alcohols (PAMA additives) are particularly highly regarded for this purpose.
The object is achieved by a copolymer according to the features of claim 1.
It was found that certain PAMAs functionalized with oxygen-containing polar groups exhibit unexpectedly good CFPP-improving efficacy. Such products are PAMAs with comonomers containing hydroxyl groups and/or ether groups, such as 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, 2-[2-(2-ethoxyethoxy)ethoxy]ethyl methacrylate, 2-ethoxyethyl methacrylate, 2-methoxyethyl methacrylate, methacrylic acid esters of ethoxylated tridecyl alcohol (oxo alcohol C13+20 C6), such as MARLIPAL 013/200 (Hxc3xcls), methacrylic acid esters of methoxypolyethylene glycol, such as Carbowax 350 or Carbowax 750 (Union Carbide), as well as the corresponding acrylate esters, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate.
The best efficacy was found with monomers containing hydroxyl groups such as 2-hydroxyethyl methacrylate. These additives also have good efficacy with regard to pour point and softening point.
The polymers usable according to the invention can be synthesized with all polymerization methods known in themselves.